A quick fitting and protection mechanism for a wire harness in a slide rail has a drag chain for the wire harness to be threaded through; a drag chain towing support connected to an upper slide rail and slidable in a slideway of a lower slide rail with the upper slide rail, where the drag chain towing support has a drag chain port, a wire harness outlet, and a first channel affording communication between the drag chain port and the wire harness outlet, where one end of the drag chain is connected to the drag chain port; a wire harness guide support having a wire harness entry, a wire harness exit, and a second channel affording communication between the wire harness entry and the wire harness exit, where the wire harness entry is in rotatable communication with the wire harness exit.